Paper sheet is finished using surface smoothing equipment capable of modifying the paper surface quality. The most typical of such machines are soft-calenders, which are principally adapted as on-machine units. Such units run at the web speed of the paper machine and have a width equal to that of the paper machine.
The rolls of calenders and presses are loaded against each other at the roll ends by means of hydraulic cylinders acting on the bearing housings of the rolls. Calenders in particular require high compressive forces which are applied or backed by the frame of the equipment, and finally, the foundation thereof. In conventional frames, the forces applied by the loading cylinders are backed almost directly by the foundation structures of the equipment, thus requiring that the foundations of the equipment be extremely strong, but nevertheless subjecting the foundation to the risk of fractures and other damage.
In a prior-art frame construction, the loading cylinder is positioned between the bottom rail of the frame and the housings of the roll end bearings. In this design, the frame is stressed at its center with a high positive support force which is directly transmitted to the foundation, while the legs of the calender frame are correspondingly stressed by negative support forces. As the calender loading forces are directly transmitted to the foundation structures, the loading force of the calender tends to dislodge the frame and thus the equipment from its foundation because the loading force imposes a direct tensional stress on the foundation anchor bolts and mounting fixtures located at the ends of the frame legs.
In another prior-art frame design, the equipment frame is shaped as a continuous U-section. The loading cylinder is mounted to the bottom rail of the U-flame, and the bottom rail is supported a distance above the floor and the foundation structures. In this design, the loading forces cause both tension and bending stresses on the mounting elements at the frame legs. The bending moment results in a torque stress which is transmitted to the anchor bolts of the frame leg ends and to the foundation, thus causing an extremely high load on the foundation structures. The loading conditions will be particularly accentuated when the nip is opened quickly, whereby the internal stresses of the frame are rapidly relieved and the direction of the forces is changed causing a high transient stress to be imparted to the foundation structures.
Wide and fast paper machines impart high static loads to the foundations, and the level of dynamic stresses is further increased by reaction forces which are transmitted to the foundation during operation of the machine.